One device that has become generally accepted and is commonly used by physicians and other health care professionals is known as a radiation thermometer, or infrared thermometer. Such devices are commercially available from Thermoscan, Inc. of San Diego, Calif. Devices of this type are described, for example, in U.S. Pat. Nos. 5,368,038 (Fraden), 4,797,840 (Fraden), 4,479,931 (Mooradian), 5,127,742 (Fraden), 5,178,464 (Fraden), 5,626,147 (Lackey), 4,895,164 (Wood), and 5,199,436 (Pompei). A radiation thermometer noninvasively detects thermal radiation from the tympanic membrane in order to determine the body temperature of the patient. A temperature reading made with this device may vary depending on the angle and depth of placement of the tip of the device with respect to the ear canal. In particular, the geometric relationship between the sensor and the tympanic membrane influences the ultimate reading by the sensor in operation. The field of view of the device, when detecting thermal radiation also affects the temperature reading. The technology described in U.S. Pat. No. 5,626,147 (Lackey) seeks to solve these problems by using a sensor geometry which has wide and narrow fields of view and a look-up table with corrective values to provide an output indicative of the body temperature.
Similar problems exist in measuring acoustic reflectance of an ear. Acoustic reflectance is measured by measuring sound waves emitted from the ear in response to a stimulus applied to the ear. The measured reflectance may be analyzed to determine the likelihood that fluid is present in the middle ear. Acoustic reflectometers are described, for example, in U.S. Pat. Nos. 4,601,295 (Teele), 4,459,966 (Teele), and published PCT Publication WO96/23293 (Combs et al.), all of which are assigned to MDI Instruments, Inc., of Woburn, Mass. Products are commercially available from MDI Instruments, Inc., under the trademarks "EARCHECK" and "EARCHECK PRO." U.S. Pat. Nos. 5,594,174 and 5,651,371 also describe a device for measuring acoustic reflectance in a manner that permits the incident and reflected acoustic signals to be separately measured. Measurements made using an acoustic reflectometer also may be affected by line of sight measurements from the tip of the device to the tympanic membrane. While the aforementioned PCT publication describes a device in which the output is substantially independent of the line of sight, the device primarily determines the likelihood that fluid is present in the ear. The device also can measure conductive hearing loss. However, in the detection of acute otitis media or severe ear infection, fluid is only one factor in a diagnosis.